Kernel-4.18.0-80.el8_arm,arch_timer

• ARM architected timer

ARM cores may have a per-core architected timer, which provides per-cpu timers,
or a memory mapped architected timer, which provides up to 8 frames with a
physical and optional virtual timer per frame.

The per-core architected timer is attached to a GIC to deliver its
per-processor interrupts via PPIs. The memory mapped timer is attached to a GIC
to deliver its interrupts via SPIs.

** CP15 Timer node properties:

• compatible : Should at least contain one of
  “arm,armv7-timer”
  “arm,armv8-timer”

• interrupts : Interrupt list for secure, non-secure, virtual and
  hypervisor timers, in that order.

• clock-frequency : The frequency of the main counter, in Hz. Should be present
  only where necessary to work around broken firmware which does not configure
  CNTFRQ on all CPUs to a uniform correct value. Use of this property is
  strongly discouraged; fix your firmware unless absolutely impossible.

• always-on : a boolean property. If present, the timer is powered through an
  always-on power domain, therefore it never loses context.

• fsl,erratum-a008585 : A boolean property. Indicates the presence of
  QorIQ erratum A-008585, which says that reading the counter is
  unreliable unless the same value is returned by back-to-back reads.
  This also affects writes to the tval register, due to the implicit
  counter read.

• hisilicon,erratum-161010101 : A boolean property. Indicates the
  presence of Hisilicon erratum 161010101, which says that reading the
  counters is unreliable in some cases, and reads may return a value 32
  beyond the correct value. This also affects writes to the tval
  registers, due to the implicit counter read.

** Optional properties:

• arm,cpu-registers-not-fw-configured : Firmware does not initialize
  any of the generic timer CPU registers, which contain their
  architecturally-defined reset values. Only supported for 32-bit
  systems which follow the ARMv7 architected reset values.

• arm,no-tick-in-suspend : The main counter does not tick when the system is in
  low-power system suspend on some SoCs. This behavior does not match the
  Architecture Reference Manual’s specification that the system counter “must
  be implemented in an always-on power domain.”

Example:

timer {
    compatible = "arm,cortex-a15-timer",
             "arm,armv7-timer";
    interrupts = <1 13 0xf08>,
             <1 14 0xf08>,
             <1 11 0xf08>,
             <1 10 0xf08>;
    clock-frequency = <100000000>;
};

** Memory mapped timer node properties:

• compatible : Should at least contain “arm,armv7-timer-mem”.

• clock-frequency : The frequency of the main counter, in Hz. Should be present
  only when firmware has not configured the MMIO CNTFRQ registers.

• reg : The control frame base address.

Note that #address-cells, #size-cells, and ranges shall be present to ensure
the CPU can address a frame’s registers.

A timer node has up to 8 frame sub-nodes, each with the following properties:

• frame-number: 0 to 7.

• interrupts : Interrupt list for physical and virtual timers in that order.
  The virtual timer interrupt is optional.

• reg : The first and second view base addresses in that order. The second view
  base address is optional.

• status : “disabled” indicates the frame is not available for use. Optional.

Example:

timer@f0000000 {
    compatible = "arm,armv7-timer-mem";
    #address-cells = <1>;
    #size-cells = <1>;
    ranges;
    reg = <0xf0000000 0x1000>;
    clock-frequency = <50000000>;

    frame@f0001000 {
        frame-number = <0>
        interrupts = <0 13 0x8>,
                 <0 14 0x8>;
        reg = <0xf0001000 0x1000>,
              <0xf0002000 0x1000>;
    };

    frame@f0003000 {
        frame-number = <1>
        interrupts = <0 15 0x8>;
        reg = <0xf0003000 0x1000>;
    };
};